Subcontractor Cascade Bridge has been building the Tillamook Overpass on a yearlong $7 million contract. Pouring concrete on a hot day in July, they used a mix that was not as fluid as they would have liked, and it came out too porous.

TriMet officials, having promised the $1.49 billion line will open to the public in 2015, said that the two-week error did not delay the project overall because they had built in time to fix quality-control issues.